Screw hole with preinstalled screw

ABSTRACT

The present invention relates to a screw hole (12) in hardware parts (10), especially in metal furniture hardware, in which is screw with a given outside thread diameter provided with a truncoconical countersink head can be preinstalled. The hole (12) has a countersink (18) matching the truncoconical head of the screw, followed by a substantially cylindrical hole section (20) for the passage of the shaft of the screw. The inside diameter of the cylindrical hole section (20) is slightly smaller than the outside diameter of the screw shaft measured across the threads of the screw (14), and into the cylindrical hole section an internal thread (24) is worked into the cylindrical hole section, where the length of the threaded shaft as measured in the screw driving direction is shorter than that of the unthreaded shaft section of the screw adjoining the bottom of the countersink head.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a screw hole in furniture fittings, especiallyin metal hardware for furniture, in which a screw provided with atruncoconical countersink head and having a thread of a given outsidediameter is preinstalled, wherein the hole has a countersink shaped tocomplement the truncoconical head of the screw and adjoined by asubstantially cylindrical section to accommodate the shaft of the screw.The invention also concerns a method for the production of such holes inhardware made of thin sheet metal.

In hardware that is to be fastened by screws to pieces of furniture,e.g., mounting plates for furniture hinges, it is common practice topreinstall the screws on the hardware part, so that when the latter ismounted on a cabinet wail the hardware part needs only to be placed atthe intended mounting position with its preinstalled screws aligned withthe holes predrilled in the furniture and the screws to be driven inwith a screwdriver. To achieve sufficient strength in the screwconnection, screws with relatively coarse threads are used, so-called"Euro screws" being increasingly used of late, the threads of which havea relatively coarse crest, which on the one hand permits the screws tobe driven with comparatively little effort into holes in wood materials,but due to the comparatively deep penetration of the threads into thewalls of the hole they can withstand heavier loading and still permitrepeated installation and removal of the hardware.

To assure that the preinstalled screws will be held securely in thepreinstallation position, i.e., will neither drop out nor tilt away fromtheir position at right angles to the hardware surface, a relativelytight fit must be provided between the top end of the screw's shaft andthe hole.

This has been accomplished in the case of thick hardware (DE-PS 34 44851) by making the wall of the hole holding the shaft of the screwslightly smaller than the outside diameter of the shaft of the screw, sothat the crests of the threads can easily penetrate into the wall of thehole during preinstallation and cut a shallow holding thread bythemselves, so to speak.

2. The Prior Art

In the case of hardware of thin sheet metal, in which the hole thus hassuch a short length that a thread holding the screw securely can hardlybe produced, a solution to this has been found (DE-PS 36 22 001) inwhich a circular area extending over about 270° is stamped out of thearea of material adjoining the hole or, more correctly, the punchedhole, and shaped out of the plane of the sheet metal to correspond tothe pitch of the screw thread. Thus a thread is formed which suffices tohold the screw, especially above-mentioned Euro screw, securely in thepunched hole. Of course, free space must be available to correspond tothe thread formed out of the plane of the material, i.e., sheet-metalhardware of this kind must be embossed at least in the area of thepunched fastening holes to form the necessary hollow space. When thescrews are driven into the corresponding holes, the unthreaded sectionat the upper end of the screw shaft adjoining the screw head and havinga diameter smaller than the outside diameter of the threads comes intothe reach of the punched thread and the screw can then turn freelywithout binding, i.e., the piece can be screwed tightly onto thecorresponding cabinet wall in the required manner.

The invention is addressed to the problem of devising a configurationfor screw holes in hardware parts which will permit securepreinstallation of flat-head screws, and which on the other hand will beusable both in hardware of great material thickness and especially inhardware of thin sheet metal, while it will be possible for the part inquestion to be forced with its bottom into tight contact with thecabinet wall without routing out the area around the mounting hole. Atthe same time the hardware piece provided with the holes in question isalso to be installable even without preassembly and with screws ofdifferent threading or smaller-shaft diameter if their heads fit intothe countersink around the hole.

Setting out from a hole of the kind described above, this problem issolved in accordance with the invention in that the inside diameter ofthe cylindrical section of the hole is slightly smaller than the outsidediameter of the screw shaft measured across its threads, and in that athread is provided in the cylindrical section of the hole to accommodatethe thread of the screw shaft, and has a length that is shorter than theunthreaded portion of the shaft adjoining the screw head. Hardware withholes thus configured can, of course, also be installed without apreinstalled, mating screw, so that flat-head screws with nonconformingshafts, e.g., of different screw pitch, different size can be used, aslong as it is certain that the head will fit into the countersink aroundthe hole. Then, if screws with an outside thread diameter that issmaller than the inside diameter of the threaded section of the hole areused, screws can also be used whose thread runs over the entire lengthof their shaft, i.e., reach all the way to their heads.

The root diameter of the thread in the cylindrical section of the holecan be less than the crest diameter of the threaded shaft, in which caseit is recommendable to configure the thread of the cylindrical sectionof the hole so that the threads of the pre-installed screw are held inthe hole with a light force fit.

The end of the substantially cylindrical, threaded hole section remotefrom the countersunk portion is expediently adjoined by a short holesection of expanding diameter, whose diameter at the bottom of thehardware piece facing away from the countersunk portion is approximatelyequal to or slightly larger than the outside diameter of the screwmeasured across the threads.

In hardware of thin sheet metal, the fastening hole is produced inaccordance with the invention such that, in the flat sheet metal blank,first a hole of small diameter is punched, and the area of the sheetmetal adjoining the hole is then forced upward to form a substantiallycylindrical projection protruding above the upper side of the metalblank, and having an inside diameter substantially equal to the insidediameter of what will later be the substantially cylindrical holesection, and then at least a portion of the cylindrical projectionraised above the upper surface of the metal blank is flared by means ofa punch with a conical face pressed into it, and then finally the threadis produced in the remaining cylindrical hole section.

The thread can be made either by a noncutting method or it can be cutinto the cylindrical hole section.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained in the following description of twoembodiments, in conjunction with the drawing, wherein:

FIG. 1 is a cross-sectional view, on a scale considerably enlarged incomparison with the actual size, through a screw hole configured in themanner of the invention and provided in a piece of hardware made fromthin sheet metal,

FIG. 2 is a cross-sectional view through a similar fastening hole in athicker piece of hardware of pressure-cast metal;

FIG. 3 is a cross-section corresponding to that of FIG. 4, in which anintermediate stage in the production of the fastening hole isadditionally drawn in broken lines, and

FIG. 4 is a side view wherein a flat-headed screw which can bepre-installed in the holes configured according to the invention isshown in a smaller scale than in FIGS. 1 to 3, but one that is stilllarger than the original size.

FIG. 5 is a cross-sectional view of the screw aligned with the hole andillustrating relative diameters;

FIG. 6 is a cross-sectional view of the hole with the screw inpreinstalled position.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 (and FIG. 3) is a considerably enlarged view of a portion of apiece of hardware of sheet steel with a fastening hole 12 made inaccordance with the invention for a flat-headed screw 14 (FIG. 4). Thehole 12 has a countersink 18 made to fit the flat head 16 of the screw14 when it is driven entirely into the mounting hole on a cabinet wallwhich is not shown. The countersink 18 is adjoined by a basicallycylindrical hole section 20 in which, however, an internal thread 24 hasbeen rolled or cut which is complementary to the thread of the threadedsection 22 of the shaft of the screw 14. The cylindrical section 20provided with the internal thread 24 is then adjoined by another short,flaring section 26 of the hole, whose diameter increases toward thebottom of the hardware piece to a size that is at least equal to orslightly larger than the outside diameter of the shaft of the screw 14measured across the threads.

The length of the threaded cylindrical hole section is shorter than ashort, unthreaded section 28 of the shaft of the screw 14 providedbetween the head 16 and the threaded section 22, and the diameter of theunthreaded section 28 of the shaft is furthermore smaller than theinside diameter of hole section 20. It is clear that pre-assembly of thescrew 16 in hole 12 is possible because the front end of the shaft isdriven into the internal thread 26 of hole section 20. If a slightlytight fit is provided between the screw and the internal thread 26, thepre-installed screw 14 will be held securely in hole 12 until it isdriven into a pre-drilled hole in the substrate upon installation.

In FIG. 2 there is represented a screw hole formed basically in the samemanner in a section made by pressure casting from metal in a hardwarepart 10'. Since identical sections of hole 12 are provided with the samereference numbers it will be sufficient here to refer to the precedingdescription of the embodiment shown in FIG. 1.

FIG. 3 corresponds to FIG. 1, but an intermediate form that the hardwarepart 10 has during manufacture is represented in broken lines. Thecountersink 18 is first formed from a cylindrical projection 30 madefirst by stamping a hole and deforming the area of the materialsurrounding the hole, this deformation being performed by forcing downinto the cylindrical projection 30 a punch having a face complementaryto the countersink. The originally cylindrical projection 30 is thusshaped to a flaring projection which can be seen in FIGS. 1 and 3. Theinternal thread 24 is then either made by a noncutting method byrotating an appropriate threading mandrel or cut by means of a threadingtap in the cylindrical section 20.

It is apparent that modifications and further developments of theembodiments described can be made within the scope of the idea of theinvention. It is to be noted that the intended hole in the caserepresented for pre-installation of so-called "Euro screws" can also bereconfigured by appropriate dimensional adaptation such that ordinarywood screws or even so-called particle board screws or Spax screws canbe pre-installed. On the other hand, hardware parts can also be fastenedwith the screws described and represented in the drawings and also withflat-head wood screws or toggle bolts or expansion plug screws. Sincethe flat head of the last-named screws is considerably larger inrelation to the shaft diameter than the flat head 16 of the Euro screwshown in FIG. 4, the shaft diameter of a wood screw suitable for thehole 12 is definitely smaller than the shaft diameter of the screw 14,so that the threaded shaft can be passed without difficulty through thehole section 20 provided with the internal thread 24. Butpre-installation of these screws of smaller shaft diameter is notpossible.

In FIG. 5, the screw 14 is shown in alignment with the hole 12, prior topreinstallation and illustrates the relative diameters and lengths ofparts of the hole and the screw. The cylindrical hole section 20 has aninside diameter D that is slightly smaller than the outside diameter d₁of the screw shaft measured across the threads of the screw 14, but yetis slightly greater than the diameter d₂ of the threadless shaft section28. The internal thread section of the hole 20 has a length L that ismeasured in the driving direction of the screw, which is shorter thanthe length 1 of the threadless shaft section 28, measured in the samedirection.

I claim:
 1. A screw hole (12) in hardware pieces (10), having apreinstalled screw provided with a truncoconical countersink head (16)and having a threaded shaft section (22) of given outside threaddiameter (d₁) and a threadless shaft section (28) between thecountersink head and the threaded shaft section, the diameter (d₂) ofwhich is smaller than the diameter of the threaded shaft section, thescrew hole (12) having a countersink (18) of a shape complementary tothe truncoconical countersink head (16) of the screw and having asubstantially cylindrical hole section (20) disposed adjacent in thecountersink for the passage of the shaft of the screw: comprisingsaidcylindrical hole section (20) having an inside diameter (D) that isslightly smaller than an outside diameter (d₁) of the screw shaftmeasured across the threads of the screw (14) and slightly greater thanthe diameter (d₂) of the threadless shaft section (28), and saidcylindrical hole section (20) having an internal thread section (24)that receives the threaded shaft (22) of the screw (14) in thepreinstalled state, wherein said internal thread section (24) has alength (L) measured in a driving direction which is shorter than length(1) of the threadless shaft section (28) of the screw (14),and whereinthe depth of the threads of the internal thread section (24) in thecylindrical hole section (20) is smaller than the height of the threadsof the threaded shaft section (22) of the screw (14).
 2. The screw holeaccording to claim 1, wherein the threads in the internal thread section(24) of the cylindrical hole section (20) are so configured that thethreads of the threaded shaft section (22) of the pre-installed screw(14) are held in the hole (12) with a light force fit.
 3. The screw holeaccording to claim 1, wherein a short hole section (26) expanding indiameter adjoins the end of the substantially internal thread section(24) opposite the countersink (18), and its diameter (D₁) at the bottomside, remote from the countersink, is approximately equal to or slightlygreater than the outside diameter (d₁) of the shaft of the screw (14).4. The screw hole according to claim 1, wherein the internal diameter(D) of the hole (20) is smaller than the outside diameter (d₂) of theunthreaded section (28) of the shaft of the screw (14).